In the medical field, an affected area in the internal organs, skeletons, or the like is photographed with, for example, X-rays for various tests and diagnoses. Through the application of the recent digital techniques, a dynamic image in which the movement of an affected area is captured with X-rays or the like can be acquired relatively easily.
The recent digital techniques can photograph a dynamic image of a subject region including a target area using a semiconductor imaging sensor such as a flat panel detector (FPD), enabling the diagnosis by motion analysis of a target area, which could not have been made in still image photographing and diagnosis by conventional X-ray photography. For example, it is studied to extract the ventilation information in a lung field from a chest X-ray dynamic image and quantitatively analyze the dynamic function from the changes in the concentration and motion of the lung field, to thereby assist diagnosis/treatment (CAD for X-ray moving images).
For example, in the image forming technology disclosed in Patent Document 1, for a subtraction image based on a difference value between two successive images in a time axis direction, successive subtraction images are created in which gradations of the newest subtraction image and the time-elapsed subtraction image are gradually changed.
In the image processing technology disclosed in Patent Document 2, any one of the maximum value, minimum value, mean value, and median value of pixel values is taken as a pixel value to generate an image for each corresponding pixel group from a plurality of subtraction images.
In the moving image processing technology disclosed in Patent Document 3, time variations at the upper and lower positions of a diaphragm are calculated from the dynamic image of a chest, and a time variation of a pixel signal value in a small block of a lung field region is calculated, to thereby generate a display with a brightness value corresponding to a phase delay time of a time variation in a small block corresponding to the time variation of the diaphragm.